Conventionally, for example, Patent Document 1 discloses a failure determination apparatus for an internal combustion engine including a variable valve operating mechanism which can halt the operations of an intake and exhaust valves in a closed state. In this conventional failure determination apparatus, an arrangement is made such that the occurrence or nonoccurrence of misfire in the internal combustion engine is determined for each cylinder based on the rotational variation of a crankshaft.
Moreover, for example, Patent Document 2 discloses a misfire determination method of a particular cylinder in a multi-cylinder engine. In this conventional misfire determination method, an arrangement is made such that when it is determined that misfire has occurred in any of the cylinders based on predetermined misfire information (the output of an O2 sensor disposed in the downstream side of the integral part of an exhaust manifold), fuel injection to each cylinder is successively stopped from one cylinder after another. Then, when misfire information becomes not to be detected by such successive stopping of fuel supply, it is determined that a misfire has occurred in the cylinder to which fuel supply is stopped.    [Patent Document 1] Japanese Laid-open Patent Application Publication No. 2003-184626    [Patent Document 2] Japanese Laid-open Patent Application Publication No. Sho 62-228640